In 3GPP Rel 8, LTE/EPC is standardized. The system includes 3GPP (3rd Generation Partnership Project) as well as non-3GPP system access. In the core network the proxy mobile IP (PMIP) protocol as well as the GTP-C protocol (GPRS Tunneling Protocol-Control) can be used as mobility control protocol. When PMIP is used, basic IP connectivity is provided in the core network between the Packet Gateway (PGW) and the user equipment by Generic Routing Encapsulation (GRE) tunneling specified in IETF. When GTP-C is used for control, GPRS Tunneling Protocol-User (GTP-U) is used as user plane for tunneling of user data in the Evolved Packet Core (EPC). Compared to the GTP mobility protocol, the PMIP protocol provides simpler and more limited functionality. In particular, the bearer handling is simplified.
The system architecture of an existing solution is shown in FIG. 1, where a user equipment 3 is connected to a Evolved Universal Terrestrial Radio Access Network (EUTRAN) 4. The system has a Mobility Management Entity (MME) providing control-plane functionality and giving orders to the Signaling Gateway (SGW). A Home Subscriber Server (HSS) is connected to the MME and describes the many database functions in the network. The Packet Data Network Gateway (PGW) 13 provides connectivity between the user equipment 3 and external networks. The Policy and Charging Rules Function (PCRF) 6 is connected between the PGW 13 and an operator's IP services 8, such as IMS, PSS etc. and takes care of policy and charging issues between the user equipment 3 and the operator. In the existing solution the core network (CN) interfaces S5/S8 can be PMIP or GTP based. The S2 interfaces are PMIP based. The PMIP based interfaces are marked with dashed lines in FIG. 1. The serving gateway (SGW) 12 or the non-3GPP access system 7 acts as an (Mobile Access Gateway) MAG, while the PGW 13 act as the local mobile anchor (LMA) using PMIP terminology.
When PMIP 16 is used, basic IP connectivity is provided in the core network between the PGW and the SGW/access network by GRE 17 tunnelling specified in IETF. When GTP-C 14 is used for control, GTP-U 15 is used as user plane for tunnelling of user data in the EPC. Recently in 3GPP, the GTP specification has been split into two specifications—one for GTP Control plane (3GPP TS 29.274) and one for GTP User plane (3GPP TS 29.281). The situation for PMIP 16 based interfaces is that the control plane is specified in 3GPP TS 29.275 and in IETF RFC 5213, while the user plane is specified in IETF Draft, “GRE Key Option for Proxy Mobile IPv6”, draft-muhanna-netlmm-grekey-option-02, work in progress, as shown in FIG. 2.
With the latest developments in 3GPP and in IETF, the GRE user plane (as well as PMIP) is getting more and more aligned to GTP, and their functions are now quite similar. The differences between GRE user plane and GTP-U are illustrated in table 1 below. The differences are in Quality of Service (QoS) and bearer handling, as well as for transport IP addressing for user plane and control plane.
TABLE 1GTP-UGRE user planeCommentTunnel idTEID (32 bit)GRE Key (32 bit)SameErroneous userErr indU-NERPSamepacketsPathEchoEchoSameManagementNode FailureRestart CounterRestart CounterSameIP addressingSeparate IPThe same IPDifferentaddress for U-address for U-plane and C-Planeplane and C-PlaneQoSDefault andOnly one bearerDifferentdedicated bearersper end user IPaddress
With the tight coupling of control and user plane in the existing solutions there may be problems when doing hand over (HO) between PMIP and GTP based interfaces. A mapping between different parameters is needed. When the user equipment changes from GTP based interface to PMIP based interface there needs e.g. to be a mapping between Tunnel Endpoint Identifier (TEID) and GRE keys for optimized hand over. It is also a need for a selection mechanism for handling the dedicated bearers and the default bearer (GTP-U) which can not be handled in the GRE tunneling network.
There is also a product problem with the known solutions of supporting multiple user planes.